The invention relates to a replaceable wearing surface for a sealing arrangement.
In presses for de-watering liquid suspensions, in particular fiber suspensions, where the presses have at least one rotatable screening drum and the de-watering takes place radially into the drum(s), the suspended material is de-watered by the liquid in the suspension passing through a perforated or slotted, often cloth-covered, surface shell of the drum(s) which is (are) arranged partly submerged in a trough containing the liquid suspension. The suspended material then forms a cake or a web on the outside of the surface, which may be cloth-covered, and is removed. New liquid suspension and, if appropriate, treatment liquid are supplied to the trough as liquid and solid material are removed by the drum(s).
The construction of such presses requires that the suspension is not allowed to escape over the end walls of the drum(s). For this reason, sealing arrangements are necessary between the drum(s) and the trough.
The sealing between the trough and the drum(s) is effected between a stationary surface and a surface in continuous motion, that is to say between generally annular or circular-segment-shaped sealing elements arranged on the trough and an annular sealing element on the drum end walls on the rotating drum(s). This means that, on account of the rotation of the drum(s) and a certain inevitable penetration of suspended material between the sealing surfaces, the sealing surfaces are subjected to wear, for which reason the sealing elements with their sealing surfaces or what are known as wearing surfaces must be easily replaceable, which means that the method of fastening the sealing elements on in particular the drum end walls is important.
The known art for fastening sealing elements on the drum end walls involves fastening by welding and/or by radial or axial screw connections through the wearing surfaces, or by shrinking, all of these fastening methods having disadvantages. It is not suitable, for example, to fasten them on the drum end walls by welding because this leads to thermal stresses in the sealing elements with dimensional changes as a consequence and moreover destroys any surface finish of the wearing surface of the sealing elements,. which results in a shortened life. Nor is it suitable to fasten them by screw connections, made axially in relation to the drum, through the wearing surfaces on the drum end wall because this on the one hand reduces the area of the wearing surfaces or alternatively means that the area must be increased and on the other hand means that the material in them must be made thicker in order to accommodate the head of the screw in the screw connection. In most cases, this means that the entire wear ring has to be replaced in spite of only a few percent of the thickness having been worn down, which results in each replacement of the wearing surface being extremely expensive.
Nor is it suitable to fasten them on the drum end walls by designing them as cover-like arrangements fastened to or on the drum shell because this reduces the de-watering surface area of the drum and moreover results in a connection which is unsuitable in terms of forces. Shrinking is not suitable either as an alternative fastening method because secure shrinking of a large thin ring is very exacting as far as tools and tolerances are concerned, which makes this method expensive.
PCT/SE98/01247 describes a sealing element in the form of a segmented sealing ring for a drum end wall intended inter alia for axial sealing between the drum end walls and a trough. The sealing ring segments are fastened by axial screw connections and welded joints. In this case, use is made of screw connections, made axially in relation to the drum, through the wearing surfaces on the drum end wall, which reduces the area of the wearing surfaces. It also results in it being necessary to demount the drum, or alternatively the parts of the housing against which the end wall seals, in order for it to be possible to demount the seal.
SE-C 501 710 and SE 93 02 898-3 describe other types of sealing arrangements in the same type of press, where sealing arrangements are arranged between a submersible part of the trough and a rigidly arranged part of the trough, that is to say between two parts which are stationary in relation to one another during continuous operation. SE-C 380 300 shows diagrammatically another seal with specific seal components without going into their construction in greater detail. In the type of press concerned, the sealing is important as the liquids which are pressed out of the fiber suspension are to be or at least are intended to be used/re-circulated in a closed system and are therefore to be recovered. Leakage in the presses means that great quantities of impure liquids have to be cleaned away around the machine and destroyed.
The present invention relates to a replaceable wearing surface for a sealing arrangement in presses with at least one rotatable press drum which de-waters fiber suspensions by the liquid in the suspension passing radially into the drum through a shell surface, which may be cloth-covered, on the drum(s), a cake or a web of the fiber material being formed on the outside of the shell surface which may be cloth-covered. The replaceable wearing surface for the sealing arrangement according to the invention constitutes part of an axial seal between the end walls of the press drum(s) and a trough in which the drum(s) is (are) partly submerged and relates to that part of this seal which is arranged on the drum end walls.
One object of the present invention is to provide a replaceable wearing surface for a sealing arrangement which is easily mountable and thus easily replaceable when the wearing surface has become unserviceable, and in which the problems of the known art described above relating to fastening the wearing surface in the sealing arrangement are eliminated. Accordingly, a sealing surface can be provided over the entire radial extent of the wear ring without fixing elements encroaching on the extent of the wearing surface.
It is also the object of the present invention to provide a sealing arrangement with a wearing surface which can be prepared in advance, for example by hard-metallization, where no finishing is required on replacement, which prolongs the life of the sealing arrangement. At the same time, the wearing surface part can be optimized for its function as a replaceable wear part.